1. Field of the Invention
The present invention relates to a processing agent for silver halide color photosensitive materials and processing method thereof. More particularly, the present invention relates to a processing agent for silver halide color photosensitive materials and method to improve fixing ability and stability of processing solution in a processing step including a fixing step of a consecutive processing step.
2. Description of the Related Art
Generally, as for the processing of silver halide color photosensitive materials (hereinafter stated as a “sensitive materials”) is comprised of a color developing step and a silver-removing (also called “desilverization”) step. The desilverization step is comprised of steps bleaching, fixing, bleaching and fixing and the like. For example, silver formed in the developing is removed by dissolving in a fixing step after being oxidized in a bleaching step with a bleaching solution. Normally, ferric ion complex salt is mainly used as the bleaching solution and a thiosulfate salt is used as the fixing solution. At present, many of the series of processes of this kind is performed in a step of continuous processing with an automatic developing machine (automatic processor). A plurality of processing tanks is provided inside the automatic processor and the photosensitive materials are transferred to each of the processing tanks with a transportation system and the developing process is being performed automatically in succession.
Incidentally, at present, automatic processors using silver halide color photosensitive materials have become diversified to match with needs of users. In order to conform with a photo-sensitive material to be used, an opening space or an amount to be mixed together of each processing tank, is particularly made different. However, in a tank used during a bleaching and fixing and/or a fixing step, a problem of declining processing quality caused by pH becoming unstable, and deteriorating stability and the like effected by the amount of oxygen and time period that each processing solution may contact with the air, remains to be solved.
In addition, an amount of processing solution used in each step is being reduced and a frequency of the processing solution being replenished is decreasing due to the effect of environmental problems. This leads to an increase in time period that the processing solution is stored in a tank, causing a problem that the thiosulfuric acid, the fixing element, decomposes to produce sulfides.
In particular, when a processing solution used in “silver-removing step” is brought into the processing tank where the following “washing step” is performed then decomposes forming a precipitate, a trouble like deterioration of image quality as white base color of photosensitive materials is being polluted and clogging of the circulation filter of automatic processors occur, which has caused a problem that the processing solution must be stabilized.
For this reason, there is a need for the production of a processing solution that can be applied to various kinds of automatic processors and can always be processed constantly.
To solve these problems, at present, countermeasures like raising pH of processing solution used in the desilverization step, applying an excessive amount of sulfite and applying sulfurous acid solution directly to the desilverization processing tank are taken.
However, in the bleaching and fixing step, ability of thiosulphate to prevent decomposition improves as having pH value of the processing solution rise, however, silver on the photosensitive materials cannot be removed completely which results in insufficient desilverization. In addition, as pH of processing liquid is raised, smell of ammonia becomes stronger and working environment worsens. In addition, even if excessive amount of sulfite is added or double quantity of sulfurous acid is poured in, for example, decomposition prevention effect will not be obtained to the same extent as the added amount of sulphite or sulfurous acid, and causes a side effect that desilverization speed slows down. Moreover, with regard to adding sulfurous acid directly, sulphite had to be added before the decomposition since adding thereof after decomposition does not produce any effects, causing a problem of inefficiency in operation.
To solve this problem, for example, as a sulfuration inhibitor, sulfinic acid type compounds are described in Japanese Patent No. 2994544 and Examined Japanese Patent Application No. 7-119981 and No. 7-66172. Further, as a pH buffer agent, imidazole type compounds are described in Unexamined Japanese Patent Application No. 8-190184, No. 5-197111, and No. 4-130432.